1. Field of the Invention
The present invention relates generally to an improved method and apparatus for detecting the existence of lead in a domestic water supply. More particularly, the invention concerns an apparatus in kit form which can be used by untrained members of the public in their own homes to test for excessive concentrations of lead in their tap water.
2. Discussion of the Prior Art
The contamination of domestic drinking water by dissolved lead is a source of great concern in the United States and other parts of the world. Although the deleterious health effects of ingested lead have been known for centuries, lead piping is commonplace in older residences, particularly those located in the eastern United States. While most newer homes now have galvanized steel, PVC plastic or copper plumbing, until very recently the copper was joined by use of lead-tin alloy solder. While solder of this composition is now being phased out, millions of newer homes still have lead-soldered plumbing.
Lead occurs in the drinking water primarily as a corrosion by-product of the materials used in residential plumbing systems. Water leaving the water treatment plant is typically relatively lead-free. However, pipes and solder containing lead are readily corroded by water, especially soft and acidic water and lead levels at the domestic user's tap can be much higher than those found at the treatment plant. Of substantial concern is the combination of copper pipes with solder containing lead now found in many households which can result in high lead levels, particularly in first-drawn water that has been in contact with the pipe for a period of time. It is now well recognized that newly-installed solder is easily dissolved, and people living in new housing, or in older housing but with new plumbing, wherein copper connections have been made with lead-tin alloy solder, are especially at risk of high levels of lead in the drinking water.
Because of the serious problems presented by lead contaminated drinking water, a method by which the average homeowner can simply and inexpensively test tap water to qualitatively determine if a high level of dissolved lead is present is desperately needed. The invention described herein fills this need by providing a simple, rapid and lead-specific test for aqueous lead in concentrations down to about five parts per million. Additionally, the detection method of the invention will not give an indicator precipitate with other common metallic ionic species in tap water, such as iron, zinc, copper, calcium and magnesium.
One well-known qualitative test for lead together with certain other metals such as copper, bismuth, and antimony consists of adjusting the pH to the region of about 0 to 2 and bubbling in hydrogen sulfide gas. If lead is present in sufficient quantity, a black precipitate (lead sulfide) is formed.
It is also known that amounts of lead on the order of four to seven parts per million can be determined by using dithizone or various instrumental methods. However, such tests require special equipment and chemicals, and often involve complicated experimental procedures. This type of test cannot easily be conducted by average persons in their own home.
Another technique for testing lead leached from pottery is disclosed in U.S. Pat. No. 3,809,537 issued to Angela A. Horine. This test involves extracting lead from the suspect pottery in an acid medium and reacting the resulting solution with an aqueous solution of sodium sulfide to produce an indicator precipitate of lead sulfide.
U.S. Pat. No. 4,125,376, issued to Razulis, discloses a test for various organic and inorganic water contaminants using a test tube with a small cube of synthetic sponge which is saturated with an indicator compound. For inorganic metal salts, the foam cube is impregnated with a solution of dithizone. A change in color of the cube indicates the presence of the salts of various heavy metals such as chromium, cobalt, lead, mercury and zinc in the water being tested. Lead chromate, thiocyanate, and sulfate were detected by a change in color of the cube from bright green to pinkish gray at a limit of 200 micrograms/liter.
None of the previously identified testing techniques are well suited for use by laymen in testing concentrations of lead in tap water.